Trickling Filters Foul Air Characteristics and Treatment with Activated Carbon Media

Foul airs generated by wastewater treatment processes are typically treated by chemical scrubbers/wet scrubbers, biotrickling filters, biotowers, and activated carbon scrubbers. Among these foul air treatment technologies, activated carbon scrubbers are generally used to remove low levels (parts per billions - ppb) organics and function as a second stage polishing treatment. However, in May 2011, the Orange County Sanitation District (OCSD) began operating a trickling filter/solid contact (TF/SC) process and the foul air from the trickling filter process was treated with one-stage activated carbon scrubber. The primary reason for using a one-stage carbon scrubber, instead of two-stage treatment, was because the design team was anticipating very minimal nuisance odor from the secondary process, and carbon media is known to be efficient in removing both vapor phase hydrogen sulfide (H2S) and low volatile organic compounds (VOC). However, as OCSD had begun operating the trickling filter system, there have been numerous odor complaints on multiple occasions. The odor is observed to be emanating from different areas within the system.The objectives of this article are to discuss the different types of activated carbon media that have been used to remove the trickling filter process odors, the frequency of carbon replacements, the effectiveness of carbon media in removing specific odorous compounds, impacts on the neighborhood, and OCSD’s efforts to mitigate the nuisance odors impacting the neighbors.